EP3798600B1 - Measuring device and method for measuring pressure - Google Patents

Description

The invention relates to a measuring device for determining a pressure in a measuring volume that holds a fluid or through which the fluid flows, according to the preamble of claim 1.

In many applications it may be desirable to detect a pressure of a fluid. It is therefore known in principle to expand flow meters with additional sensors for pressure measurement. However, using separate sensors for pressure measurement increases the complexity of the flow meter and thus also the costs and, under certain circumstances, the space required.

A method for determining the pressure of a fluid that does not require additional sensors when used in an ultrasonic flow meter is known from the publication DE 10 2017 005 207 A1 known. Here, a transit time of an ultrasonic wave from a transmitting to a receiving ultrasonic transducer is recorded for two different excitation frequencies. Depending on the difference between these transit times, the pressure in the fluid can be determined. Preferably, the transit time difference for waves with different excitation frequencies is determined and taken into account for both directions of propagation. Since at least two sequential measurements for different excitation frequencies, typically even four sequential measurements for the two excitation frequencies and propagation directions, are required in the method explained, relatively small pressure or flow rate changes between the measurement intervals used lead to a relatively strong disturbance of the measurement, which means that the pressure determined is very noisy, at least in some applications.

Further state of the art is out WO 2018/219492 A1 and EP 3 492 878 A1 known. The invention is therefore based on the object of specifying an approach for determining a pressure that is improved in comparison thereto, which is in particular less susceptible to faults and can nevertheless be implemented with little technical effort.

The object is achieved according to the invention by a measuring device according to claim 1 .

In the context of the invention, it was recognized that particularly when the wave is coupled directly into the fluid or decoupled from it by the respective vibration converter, but also in the case of indirect excitation of the wave via excitation of the side wall of the measuring volume, a pressure in the Fluid deforms or biases the respective vibration converter. As a result, certain sub-patterns of the vibration pattern of the or the additional vibration transducer caused by the wave or the resulting output signals of the vibration transducer depend on the corresponding deformation or strain and thus on the pressure. For example, the vibration pattern can be at least a quasi-periodic vibration, with the length of the determined vibration period or a specific partial period, according to the invention the time between two successive zero crossings of the vibration, varying depending on the pressure occurring. Since, for example, in flow meters, times of zero crossings of an oscillation or the like are often to be recorded anyway in order to determine the propagation time of a wave between two oscillation converters, the measuring device according to the invention can, under certain circumstances, be used without changing the sensors of a known flow meter by a relatively simple adjustment of the measuring electronics or .Software to be implemented.

The measurement volume can be delimited by at least one side wall, with the vibration converter and the further vibration converter being arranged on the same side wall or on different side walls of the measurement volume. The side wall or side walls can be formed in particular by a measuring tube. This can be, for example, the measuring tube of a flow meter, with the flow meter For example, can determine the flow depending on a transit time of the wave between the vibration converter and the other vibration converter. In this case, no further sensors are required to additionally determine the pressure.

The vibration converter can couple the wave directly into the fluid or the vibration pattern can be transmitted directly through the fluid to the vibration converter or the further vibration converter. Alternatively, it is also possible for the vibration converter to initially excite a vibration of the side wall of the measurement volume, in particular a guided wave, e.g. a Lamb wave, in the side wall, which in turn excites the wave in the fluid. Correspondingly, it is also possible that the wave initially stimulates a vibration of the side wall, in particular a guided wave in the side wall, when it hits the side wall, which vibration is then transmitted to the vibration converter or the further vibration converter in order to stimulate it to oscillate.

The output signals of the or the further vibration converter, which relate to the vibration pattern, oscillate around a reference value, the time duration being determined as the time interval between two changes of sign of the difference between the output signal and the reference value. The output signal can in particular be a voltage signal or a current signal. In particular, the reference value can be zero, with which the duration is determined as the time interval between two sign changes of the output signal, ie between two zero crossings of the output signal. According to the invention, the time duration is determined in such a way that the time duration is determined as the time interval between two consecutive changes of sign or zero crossings.

If the procedure described is applied to a sinusoidal oscillation or a similar oscillation, for example, the duration of the positive or negative partial period can be used to determine the pressure.

A large number of approaches are known for detecting sign changes or zero crossings of output signals from oscillation converters or differences between these output signals and reference values. For example, corresponding Zero crossings or sign changes are detected using comparators that provide trigger signals for reading or resetting a counter for the time interval. Corresponding comparators and/or counters can be implemented as separate components, but can also be integrated, for example, in a microcontroller or the like. Alternatively, it would also be possible, for example, to sample the output signal by analog-to-digital conversion and to find the zero crossings or sign changes in the resulting digital data.

The pressure in the measurement volume and the resulting strain or deformation of a vibration converter can affect the duration in many ways depending on the specific design of the vibration converter and the arrangement on the measurement volume and depending on the excitation pattern used for the vibration converter. For example, a deformation or strain can lead to a non-linearity of the vibration pattern or the output signal with regard to the pressure fluctuations caused by the wave in the fluid. In particular, if an excitation pattern with sharp jumps, for example with a phase or amplitude jump to mark a specific oscillation period, is used, the transmission of corresponding pressure transients to the oscillation converter or the additional oscillation converter can result in somewhat different oscillation patterns and thus lead to different periods of time.

However, a particularly clear and over a certain pressure range typically even approximately linear relationship between pressure and duration can result in a deformation of a vibration converter due to pressure, for example a deformation of a piezoelectric vibration converter, leading to a constant offset of the output signal. However, in the case of a sine wave or a large number of other oscillations, for example, such an offset results in the length of time for which the output signal is positive or above a reference value being lengthened, while the time for which the output signal is negative or below a reference value is shortened or vice versa. Since, for example, a sine wave in the area of the zero crossing changes approximately linearly over time, there is an approximately linear relationship between the change in the duration of the corresponding partial period, ie the partial pattern, and the offset for offsets that are not too large. With the appropriate structure of the vibration converter an approximately linear relationship between the change in duration and the pressure can thus also result.

In principle, it would also be possible to measure a corresponding offset directly, for example by analog-to-digital conversion of the output signal, but this would require the output signal to be recorded with high resolution, which can increase the outlay for implementing the measuring device. In many applications, for example if the measuring device is to be used to determine a flow rate at the same time, it may be possible to detect changes in sign or zero crossings with high time resolution anyway, so that good detection accuracy can also be achieved with regard to pressure without additional measuring effort.

The control device can be set up to control the oscillation converter with a predefined excitation pattern that includes several oscillation cycles of an oscillation, in particular a sinusoidal oscillation, with a selected one of the oscillation cycles being marked by a phase change, in particular a phase jump. In this case, the excitation pattern can be a periodic oscillation with, in particular, a fixed frequency, in particular apart from the phase change and/or an enveloping or window function for limiting the length of the excitation pattern. The vibration pattern of the or the additional vibration transducer can essentially correspond to the excitation pattern with a certain time delay, which can result in particular from the propagation time of the wave in the fluid. Deviations can occur in particular in the area of the phase change due to the dispersion relation of the fluid or due to the transient behavior of the vibration converter or the additional vibration converter.

The marking of the selected oscillation cycle by a phase change can be used in particular to determine a propagation time of the wave from the oscillation converter along the propagation path back to the oscillation converter or to the further oscillation converter, which can be used, for example, to determine a flow through the measurement volume or a fluid property To detect, for example, a temperature of the fluid. The selected oscillation cycle can be identified, for example, by the fact that the phase jump or phase change means that the selected oscillation cycle is longer or shorter than the other oscillation cycles, which, for example, as explained above, is determined by determining time intervals between zero crossings or sign changes of the output signal or the difference between the output signal and a reference value can be detected.

The predetermined partial pattern of the oscillation pattern can depend on the excitation pattern in the selected oscillation cycle. In other words, the excitation pattern in the selected oscillation cycle can be transmitted via pressure fluctuations as a wave via the propagation path back to the oscillation converter or to the further oscillation converter, with at least part of these pressure fluctuations leading to the partial pattern of the oscillation pattern. In particular, a window for the acquisition of measurement data can be selected such that the time at which the selected one of the oscillation cycles is received is within this time window, so that the measurement data relate to this selected oscillation cycle or at least part of this selected oscillation cycle, with the phase jump or phase change in particular lies within this measurement window or limits it. For example, one of the sign changes, the time interval between which, as explained above, can specify the time period from which the pressure is determined, can be caused by the phase jump or the phase change.

The control device can be set up to determine a detection time at which the partial pattern is detected and to determine a flow rate or a flow volume of the fluid through the measurement volume as a function of the detection time. In particular, as explained above, the partial pattern can correspond to the selected oscillation cycle or a partial cycle of the selected oscillation cycle or, in particular, can begin or end with the phase change or the phase jump. Thus, for example, a change of sign or zero crossing of the output signal or the difference between the output signal and the reference value at the beginning or end of the selected oscillation cycle or at the time of the phase change or the phase jump can be used to determine a propagation time of the wave from the oscillation converter to the other oscillation converter to determine. If this is done for both directions of propagation, a flow rate can be determined from the transit time difference as usual, or a flow volume can be determined using the known measurement geometry of the measurement volume.

An exemplary implementation for this will be explained below. In this case, to avoid unnecessary repetitions, a zero crossing or sign change of the output signal or the difference between the output signal and the reference value is used abbreviated as zero crossing. Two time counters can be reset at the point in time at which the phase change or the phase jump is output as part of the excitation pattern to the oscillation converter or at a point in time with a defined time position with respect to this point in time. A first of these time counters can be read out and reset for each detected zero crossing or each detected zero crossing with a specific direction. The value read from the time counter then describes the duration of an oscillation cycle or the positive or negative half of an oscillation cycle. Due to the phase change in the selected oscillation cycle, this or its positive or negative partial oscillations have a different length and can therefore be recognized. In this case, the value of the second time counter can be read out, ie that time counter which is not reset at each zero crossing, in order to determine the propagation time of the wave to the oscillation converter or the further oscillation converter. As explained above, this can be used, for example, to determine a flow volume or the like based on a transit time difference between propagation directions. Since the value read from the first time counter, in particular when it is recorded for positive or negative halves of oscillation, is also related to the pressure, as explained above, the pressure can be determined from this value.

The approach explained above assumes that the duration of the selected oscillation cycle is at least approximately known, so that the duration of the recorded cycle or the value of the first time counter can be used to immediately recognize that the selected oscillation cycle or a partial oscillation thereof is currently being recorded would. Alternatively, it would also be possible, for example, to compare values of the time counter that were recorded in succession over time, in order to identify the presence of the selected oscillation cycle or the like based on a significant deviation in the counter value.

As explained above, the value read from the first time counter correlates with the pressure. A corresponding relationship can be determined, for example, by a calibration measurement for a specific measuring device or for a specific type of measuring device. For example, a corresponding relationship can be described using a look-up table, or a mathematical relationship between the pressure and the counter value can be determined, for example by means of a regression analysis of a number of measurements.

The measuring device can be a flow meter, in which case the control device can be set up to determine a transit time difference between a first transit time of the wave from the vibration converter to the further vibration converter and a further transit time of a further wave excited by the further vibration converter to the vibration converter and from the transit time difference the to determine flow. The pressure measurement described above can be used particularly advantageously in a flow meter, since at least in the case of the type of transit time determination explained above, all the information required for determining the pressure is already available anyway. A flow meter can thus be used in addition to pressure measurement, for example, with a pure software update and a corresponding calibration.

The pressure can be determined from precisely one time period of precisely one predetermined sub-pattern. In this way it can be achieved that the pressure determination cannot be disturbed or only insignificantly even in operating situations in which sudden changes in pressure or flow are to be expected due to the short measuring time.

In addition to the measuring device according to the invention, the invention relates to a method for determining a pressure in a measuring volume receiving a fluid or through which the fluid flows.

Fig. 1

ein Ausführungsbeispiel einer erfindungsgemäßen Messeinrichtung, durch die ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens ausführbar ist,

Fig. 2

ein Anregungsmuster für einen Schwingungswandler und das Ausgangssignal eines weiteren Schwingungswandlers in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens, und

Fig. 3

beispielhafte Messdaten für ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens.

Further advantages and details of the invention result from the following exemplary embodiments and the associated drawings. Here show schematically:

1

an exemplary embodiment of a measuring device according to the invention, by means of which an exemplary embodiment of the method according to the invention can be carried out,

2

an excitation pattern for a vibration converter and the output signal of a further vibration converter in an exemplary embodiment of the method according to the invention, and

3

exemplary measurement data for an embodiment of the method according to the invention.

1 1 shows a measuring device 1 for determining a pressure in a measuring volume 2 through which a fluid flows. The fluid can in particular be a liquid, for example water, or a gas. In the example shown, the measuring device 1 is a flow meter which is used to record a quantity of liquid flowing through the measuring volume 2 . For this purpose, a transit time of a wave 6, which is excited by the vibration converter 4, is detected by a control device 10 along the propagation path 7 to the further vibration converter 5. A flow rate is determined as a function of the transit time difference between this transit time and the transit time of a wave guided in the opposite direction, as is known in principle from the prior art. In the example shown, the wave 6 is deflected by the reflectors 8, 9 in order to guide it along the propagation path 7.

When it strikes the further oscillation converter 5, the wave 6 excites an oscillation of the further oscillation converter 5 with a specific oscillation pattern. The measuring device 1 makes use of the fact that by measuring a time duration of a predetermined partial pattern of this oscillation pattern as measurement data, as described below with reference to FIG 2 will be explained in more detail, a pressure in the measuring volume 2 can be determined. Such a pressure measurement is particularly advantageous in a flow meter, ie the measuring device 1 shown, since existing sensors can be used and the pressure can be determined by simply adapting the data processing in the control device 10 . In principle, it would also be possible to carry out the pressure measurement described independently of a flow measurement. In this case, it would also be sufficient to use only one vibration converter 4, to which the wave 6 is fed back along the propagation path 7. For example, if the reflector 8 is omitted, the wave 6 could be reflected back to the vibration converter 4 on the opposite side wall 3 of the measurement volume will. In this case, only the duration of the partial pattern could be evaluated in order to measure a pressure. In principle, however, a running time could also be determined, for example in order to determine a fluid temperature or another fluid property.

2 12 shows the time course of an excitation pattern 11 with which the oscillation converter 4 is controlled by the control device 10. The excitation pattern 11 can be, for example, a voltage profile that is applied to a piezoelectric element used as a vibration converter 4 . Here are in 2 three oscillation cycles 12, 13, 14 of a sinusoidal oscillation are shown as an exemplary excitation pattern 11, a selected oscillation cycle 13 being marked by the fact that a phase change 15, in the example a phase jump, takes place within this oscillation cycle 13. A phase jump of approximately 180° is shown here, although other phase changes could also be used. In real excitation patterns 11, more than three oscillation cycles are typically used and the amplitude of the oscillation cycles is modulated by an envelope or window function.

2 FIG. 12 also shows schematically an output signal 16 of the vibration converter 5 after the corresponding shaft 6 has entered the vibration converter 5. FIG. The output signal 16 would actually be offset by the travel time of the wave 6 along the propagation path 7 to the excitation pattern 11 . For clarity, the initial pattern was 16 in 2 shifted to the left by this transit time, so that the excitation pattern 11 and the output signal 16 are shown in the same time interval. In 2 there is also a simplified representation of the output signal 16, in which distortions and other influences on the output signal 16 due to non-linearity of the vibration transducers 4, 5, the dispersion in the fluid and due to a bias of the vibration transducers 4, 5 due to the pressure in the measuring volume 2 are not taken into account.

The only effect of the pressure in the measuring volume 2 is in 2 the offset 17 of the output signal 16 is shown. This results from the fact that, for example, a vibration transducer 5 based on a piezoelectric element ultimately represents a pressure or force sensor, with its output signal 16 having a DC voltage component that corresponds to offset 17 and that depends on the pressure in measuring volume 2, and an AC voltage component that is caused by the incoming wave 6 is caused includes. Consequently the output signal 16 continues to oscillate around a reference value 18, for example 0 V, but this oscillation is asymmetrical due to the offset 17.

The control device 10 is set up to detect zero crossings or sign changes 19, 20 of the output signal 16 or the difference between the output signal 16 and the reference value 18, for example with the aid of a comparator which triggers the reading of a time counter. In this way, the durations 21 to 24 for different sub-patterns 25 to 28 of the output signal 16 or of the oscillation pattern 29 described by this can be determined. On the one hand, these time durations 21 to 24 can be used to identify the partial patterns 25, 26 that belong to the selected oscillation cycle 13, since their time durations 21, 22 differ significantly from the time durations 23, 24 of the partial patterns 27, 28 due to the phase jump 15. In this way, for example, the point in time at which the phase jump or phase change 15 reaches the further oscillation converter 5 can be clearly determined, with which the propagation time of the wave from the oscillation converter 4 to the further oscillation converter 5 can be determined with high accuracy. This can be used, for example, to determine a transit time difference as explained above.

In addition, as in 2 it can be seen that an increase in the offset 17 results in the time duration 21 for the sub-pattern 25 becoming longer and the time duration 22 for the sub-pattern 26 becoming shorter. The length of time 21 or 22 or a combination of these lengths of time, for example a difference, can thus be used to draw conclusions about the offset 17 and thus about the pressure in the measuring volume 2 . For this purpose, a look-up table or a mathematical relationship between the duration 21 or 22 and the pressure can be defined, for example, by a previous calibration of the measuring device 1 or of a group of identical measuring devices 1 . If, as in the example shown, a sinusoidal oscillation is used for excitation, the change in the duration 21 to 24 is approximately linearly dependent on the offset 17 and thus, for example in the case of piezoelectric transducers, in particular also on the pressure.

As already explained above, the pressure in the measuring volume 2 can also lead to distortions in the output signal 16 or the oscillation pattern 29 or to a change in the transient behavior, in particular in the area of the phase change 15 . These effects can make an additional contribution to changing the time durations 21, 22 with the pressure, so that the procedure described may can achieve higher accuracy in the pressure detection than would be possible solely with the previously explained detection of the offset 17 over the time periods 21, 22.

Compared to a direct measurement of the offset 17, the advantage is also achieved that the pressure measurement can be carried out as part of a normal flow measurement and not only in idle phases when no flow measurement is taking place. In addition, with the procedure described, it is not necessary to detect specific values for the output signal 16, but it is sufficient to recognize the sign changes 19, 20 or zero crossings. The procedure can thus be implemented easily and, in particular, conventional flow meters can be modified with little effort, for example by means of a pure software update, in order to carry out the method described.

3 shows measurement data 33 of an example measurement of the pressure based on a time duration of a specific received partial pattern or for the time interval between two sign changes of the difference of the output signal 16 and the reference value 18. The lower X-axis 30 shows the number of the current measurement, the Y-axis 31 the value of a time counter, which is set at the beginning of the in 2 sub-pattern 26 shown is reset and read out at the end of which, and the upper X-axis 32 shows pressure values that are set during a respective high-pressure interval 34 . Between the high-pressure intervals 34, the pressure in the measurement volume 2 is lowered back to normal pressure during a normal-pressure interval 35 in each case. As in 3 As can be clearly seen, the measurement data 33, that is to say the respective durations 22 of the partial pattern 26, are a good measure of the pressure, with the duration 22 varying approximately linearly with the pressure.

Reference List

1

measuring device

2

measurement volume

3

Side wall

4

vibration converter

5

vibration converter

6

Wave

7

propagation path

8th

reflector

9

reflector

10

control device

11

excitation pattern

12

vibration cycle

13

vibration cycle

14

vibration cycle

15

phase change

16

output signal

17

offset

18

reference value

19

change of sign

20

change of sign

21

duration

22

duration

23

duration

24

duration

25

part pattern

26

part pattern

27

part pattern

28

part pattern

29

vibration pattern

30

X axis

31

Y axis

32

X axis

33

measurement data

34

high pressure interval

35

normal pressure interval

Claims (7)

1. Measuring device for determining a pressure in a measurement volume (2) which receives a fluid or through which the fluid flows, wherein an oscillation transducer (4) of the measuring device (1) is arranged on the measurement volume (2), wherein a control device (10) of the measuring device (1) is set up to activate the oscillation transducer (4) for exciting a wave (6) in the fluid, wherein the oscillation transducer (4) is set up and arranged on the measurement volume (2) in such a way that the wave (6) is returned along a propagation path (7) to the oscillation transducer (4) or to at least one further oscillation transducer (5) of the measuring device (1) arranged on the measurement volume (2), wherein the control device (10) is set up to record measurement data (33) concerning an oscillation pattern (29) of the or the further oscillation transducer (4, 5) that is excited by the wave (6) and to determine the pressure in the measurement volume (2) on the basis of the measurement data (33), characterized in that the control device (10) is set up to determine as measurement data (33) a time period (21-24) of a predetermined sub-pattern (25-28) of the oscillation pattern (29) and, from the time period (21-24), the pressure in the measurement volume (2), wherein output signals (16) of the or the further oscillation transducer (4, 5) concerning the oscillation pattern (29) oscillate about a reference value (18), wherein the time period (21-24) is determined as a time interval between two temporally successive changes in sign (19, 20) of the difference between the output signal (16) and the reference value (18).
2. Measuring device according to Claim 1, characterized in that the control device (10) is set up to activate the oscillation transducer (4) with a predetermined excitation pattern (11), which comprises multiple oscillation cycles (12-14) of an oscillation, in particular a sinusoidal oscillation, wherein a selected one of the oscillation cycles (13) is marked by a phase change (15), in particular a phase jump.
3. Measuring device according to Claim 2, characterized in that the predetermined sub-pattern (25, 26) of the oscillation pattern (29) depends on the excitation pattern (11) in the selected oscillation cycle (13).
4. Measuring device according to Claim 2 or 3, characterized in that the control device (10) is set up to determine a recording time at which the sub-pattern (25, 26, 27, 28) is recorded and to determine a flow rate or a flow volume of the fluid through the measurement volume (2) on the basis of the recording time.
5. Measuring device according to one of the preceding claims, characterized in that the measuring device (1) is a flowmeter, wherein the control device (10) is set up to determine a difference in transit times between a first transit time of the wave (6) from the oscillation transducer (4) to the further oscillation transducer (5) and a further transit time of a further wave, excited by the further oscillation transducer (6), to the oscillation transducer (5) and to determine the flow from the difference in the transit times.
6. Measuring device according to one of the preceding claims, characterized in that the pressure is determined from exactly one time period (21-24) of exactly one predetermined sub-pattern (25-28).
7. Method for determining a pressure in a measurement volume (2) which receives a fluid or through which the fluid flows, wherein an oscillation transducer (4) is arranged on the measurement volume (2), wherein the oscillation transducer (4) is activated for exciting a wave (6) in the fluid, wherein the wave (6) is returned along a propagation path (7) to the oscillation transducer (4) or to a further oscillation transducer (5) arranged on the measurement volume (2), wherein measurement data (33) which concern an oscillation pattern (29) of the or the further oscillation transducer (4, 5) that is excited by the wave (6) are recorded, and wherein the pressure in the measurement volume (2) is determined on the basis of the measurement data (33), characterized in that a time period (21-24) of a predetermined sub-pattern (25-28) of the oscillation pattern (29) and, from the time period (21-24), the pressure in the measurement volume (2) are determined as measurement data (33), wherein output signals (16) of the or the further oscillation transducer (4, 5) concerning the oscillation pattern (29) oscillate about a reference value (18), wherein the time period (21-24) is determined as a time interval between two temporally successive changes in sign (19, 20) of the difference between the output signal (16) and the reference value (18).

Images